In the LTE (Long Term Evolution) scheme and the LTE-Advanced scheme, PUCCH (Physical Uplink Control Channel) is defined as a control channel for transmitting uplink control information (UCI (Uplink Control Information)). As the uplink control information transmitted by using PUCCH, there are, for example, CQI (Channel Quality Indicator) that is channel quality information, ACK/NACK that is acknowledgement information for a data signal transmitted in downlink, and a scheduling request (SR: Scheduling Request) that is transmitted when a data signal to be transmitted in uplink occurs.
Also, in the LTE-Advanced scheme, a user apparatus UE and a radio base station eNB are configured to be able to perform CA (Carrier Aggregation) by using a plurality of cells.
When CA is performed, the user apparatus UE is configured with a PCell (Primary cell) that is a cell having high reliability for securing connectivity and an SCell (Secondary cell) that is an ancillary cell. First, the user apparatus UE connects to the PCell, and can add an SCell as necessary. The PCell is a cell similar to a cell of the LTE scheme supporting RLM (Radio Link Monitoring), SPS (Semi-Persistent Scheduling) and the like. It is necessary to perform handover processes for changing the PCell of the user apparatus UE.
The SCell is configured in the user apparatus UE by being added to the PCell. Addition and deletion of the SCell is performed by an RRC (Radio Resource Control) signaling. The SCell is in an deactivated state right after it is configured in the user apparatus UE. Thus, the SCell is a cell that can be used for communication (scheduling can be performed) only after activating the SCell in an MAC (Media Access Control) layer.
Also, in the LTE-Advanced scheme, PUSCH-PUCCH simultaneous transmission is available in which a PUCCH and a PUSCH (Physical Uplink Shared Channel) for transmitting data are transmitted simultaneously. The meaning of the PUSCH-PUCCH simultaneous transmission includes both of PUSCH-PUCCH simultaneous transmission within the same cell and PUSCH-PUCCH simultaneous transmission in a plurality of cells.
A carrier corresponding to a cell in CA is called a CC (Component Carrier). In each cell in CA, a cell corresponding to an uplink can be called a cell for uplink, and a cell corresponding to a downlink can be called a cell for downlink. Also, “transmit/receive a signal in a particular cell” means “transmit/receive a signal using a component carrier corresponding to the cell”.
In the LTE scheme, the uplink control information is normally transmitted from the user apparatus UE to the radio base station eNB via a PUCCH. In a predetermined case, the uplink control information is transmitted by using a PUSCH that transmits data in a normal case. This is called piggyback.
Referring to FIG. 1, examples of a case where piggyback is performed and a case where piggyback is not performed are described.
FIG. 1 (a) shows a normal case in which CA is not configured. FIG. 1 (a) shows that uplink control information is transmitted by a PUCCH when a PUSCH is not assigned at a transmission timing of the uplink control information.
FIG. 1 (b) shows a case in which CA is not configured, and shows that uplink control information is transmitted by a PUSCH when the PUSCH is assigned (that is, in a case when the user apparatus receives a scheduling grant, and is assigned a radio resource so that the user apparatus can transmit data) at a transmission timing of the uplink control information. Even when the PUSCH is assigned, if the user apparatus UE is configured with PUSCH-PUCCH simultaneous transmission, the UE transmits uplink control information by using a PUCCH. But, if the user apparatus UE is not configured with PUSCH-PUCCH simultaneous transmission (including a case where the user apparatus UE does not have an ability of PUSCH-PUCCH simultaneous transmission), the UE transmits uplink control information by using the assigned PUSCH.
FIG. 1 (c) shows a case where CA is configured and, at a transmission timing of uplink control information, a PUCCH is configured on PCell, a PUSCH is configured on SCell, and PUSCH-PUCCH simultaneous transmission is available. In this case, the uplink control information is transmitted by the PUCCH of the PCell.
FIG. 1 (d) shows a case where CA is configured and, at a transmission timing of uplink control information, a PUSCH is configured on SCell, and PUSCH-PUCCH simultaneous transmission is not available. In this case, the uplink control information is transmitted by the PUSCH of the SCell.